To isolate the problem, switch to the default theme, deactivate all plugins and then add the plugins one by one until the problem pops up again. It may also be a problem with your theme, but it’s more likely it’s a plugin problem.

Downloading these files does slow down the “logged in” page compared to the “not logged in” page, but that’s a choice made by the maker of the theme for this site. It’s not a problem with the core software.

thousande, you have to create a new theme (under /my-templates/) and then edit the header.php file in your new theme so that it doesn’t have the stuff inside this loop starting with <?php if ( is_topic() && bb_is_user_logged_in() ) : ?>

Actually, I think that bbPress doesn’t even currently support AJAX posting, so all those files are unneeded.